Intracarotid injection of the neurotoxin, 1-methyl-4-phenyl-1,23,6- tetrahydropyridine (MPTP), produces unilateral destruction of the dopaminergic cells of the ipsilateral substantia nigra pars compacta in primates. The deoxyglucose method has been used in these experiments to map the neural circuits involved in the treatment of these hemiparkinsonian monkeys with dopaminergic agonist drugs and with dopaminergic implants. Comparisons of the alterations in metabolic activity associated with L-DOPA and apomorphine treatment reveal that these drugs produce their therapeutic effects through different neural pathways. The deoxyglucose method was also used to assess the functional recovery in hemiparkinsonian monkeys with dopaminergic implants. The pattern of glucose utilization seen in monkey with adrenal implants in which no recovery of voluntary movement was observed was identical to that seen in untreated hemiparkinsonian monkeys. In contrast, following fetal mesencephalic implants, recovery of motor function was evident along with reversal of the glucose utilization changes associated with hemiparkinsonism.